Scott Hartman's Skeletal Drawing.comhttp://www.skeletaldrawing.com/Sat, 19 Nov 2016 22:34:05 +0000en-USSite-Server v6.0.0-9609-9609 (http://www.squarespace.com)A blog on dinosaur anatomy and reconstructing the appearance of prehistoric <br/>animals.Taking a 21st century look at DimetrodonScott HartmanSat, 19 Nov 2016 23:30:17 +0000http://www.skeletaldrawing.com/home/21stcenturydimetrodon51bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:5830d35d9de4bb0ca853be11Today I have something I’m excited to share with you: my skeletal
reconstruction of Dimetrodon grandis. It looks quite a bit different from
existing skeletal reconstructions, so I’m also going to take a more
in-depth look at the underlying data. But first, let’s take a look...Today I have something I’m excited to share with you: my skeletal reconstruction of Dimetrodon grandis. It looks quite a bit different from existing skeletal reconstructions, so I’m also going to take a more in-depth look at the underlying data. But first, let’s take a look:

Why Dimetrodon? Aside from the fact that it’s awesome?! OK, I admit that without external impetus I would probably not have gotten around to working on any pelycosaur skeletal reconstructions for a fair bit yet. But for the last year I’ve been working with Permia to help them design paleo-themed clothes and merchandise, and one of their early requests was for a skeletal reconstruction of the iconic sail-backed stem-mammal.

So how does the new skeletal differ from past reconstructions? There are quite a few ways, but for now I’ll highlight three of them: The sail with semi-emerging spines, the curvature of the back, and the high-walk pose. Let’s unpack each one:

Sail shape: If you look at recent Dimetrodon paleoart you will see there has been a big increase in the variety of ways in which the sail is being restored. Some have the spines almost entirely protruding while others have the sail covering the entire thing, and almost everything in between. Much of this interest has stemmed from research done by Rega, et al., (2012) that looked at the pathologies found in the tall back spines of Dimetrodon.

The authors observed that some of the neural spines had broken and later healed. This is strongly suggests that at least part of the spine was embedded in a sail (or similar tissue) that kept them in place after breaking so they could heal. But they also observed that the tops of the spines were often bent, sometimes severely, which suggested that the top of the spines were not embedded in a sail. Further confirmation of this “emerging from the sail” configuration comes from the surface texture of the neural spines. The spines shift from a roughened texture where they are embedded in back muscles, to a texture consistent with being in a sail (e.g. impregnated with Sharpey’s fibers), to a smooth texture at the top, where they most likely became spines that stuck out of the sail.

So it appears that Dimetrodon had a serrated, multi-spined sail in life, though exactly how much of the neural spines stuck out isn’t entirely clear - the specimen discussed above came from a different species of Dimetrodon, D. giganhomogenes, and the condition may have varied between species, or possibly even within a species between genders and/or during ontogeny.

A work in progress snapshot of the dimetrodon neck and

Back curvature: If you want to know what an extinct organism looked like in life, the shape of the vertebral column is one of the most important things to get correct. Based on the many existing skeletals I had assumed that there was no controversy to be found here, as they all showed a generic series of gently arched back vertebrae with a straight neck and tail. But as I worked to restore the backbone of D. grandis I was immediately vexed, as many of the vertebral bodies (the centra) were quite strongly bevelled, which generally indicates curvature in the spine. Moreover, they weren’t curved randomly, they instead curved down in the neck and the posterior part of the back, and up at the transition from the back to the neck - in other words, they were curved in the same manner as seen in more advanced therapsids (and in many mammals). I spent a really long time on the neck and back - coming from a background based on archosaurs, and with every skeletal of Dimetrodon ever done seeming to show something else I triple-checked everything.

A couple of things have made me comfortable with this solution - first was that the neural spines themselves support it. If I forced the backbone to look like other skeletals the neural spines ended up clumping together in the areas that should be curved down. If I let them articulate the way the bones suggest then the spines maintain a reasonable, even spacing down the body. Another thing that helped convince me looking at other specimens; my skeletal is predominantly based on the Smithsonian specimen of D. grandis, but looking at other specimens I saw evidence of these same curves in several other specimens - for example in the AMNH D. incisivus specimen the same curve in the back just ahead of the hips is quite obvious (in some mounts you can see gaps between the vertebrae that were created when the back was straightened out).

The odds seem small that this bevelling of the vertebrae could be diagenetic (that is, deformation caused after burial) since the neural spines would have to also be bent to compensate. The fact that is appears in many other specimens also makes it more likely that this is a real phenomena, and not an artifact from a single specimen. As a final bit of positive reinforcement, I chatted with several Permian synapsid researchers at SVP in October and received only positive feedback. Phew!

Photo by Vicky baldwin, From Wikimedia Commons

The high walk pose: OK, I admit it, it’s a “high run” pose. By “high walk” I was referring to the semi-sprawled gait we see at times in extant crocodilians. Traditionally Dimetrodon has been portrayed using a lizard-like sprawl, but in the last couple of decades researchers have discovered trackways given the name Dimetropus. These trackways, which appear to have been made by Dimetrodon or a synapsid closely related to Dimetrodon, show an animal moving with a more upright posture, holding its belly and tail well clear of the ground.

It seems clear that Dimetrodon could sprawl when it wanted to (perhaps while at rest, or simply when it wanted to stay close to the ground), but the trackways also attest to frequent use of a more upright (semi-sprawling) posture. And if Dimetrodon was in a hurry, the more upright pose seems like the clear stance to adopt. Keen observers will note that I have actually spent a lot of time reposing my theropod skeletals to make them not be running. I’m not having a change of heart - like other skeletal poses I created for Permia this is a one-off pose for them. It’s a reasonable-yet-dynamic pose that hopefully helps make for desirable clothing and other other items, but it is specifically for their merchandise. As soon as time allows I’ll release a more general pose that will be sauntering at a more sedate pace (that is the one I will upload to my galleries).

False consensus & other thoughts: When I began this skeletal reconstruction I thought this would be an easy project, since Dimetrodon skeletals up until now have looked more or less the same. Now that I’ve spent a serious chunk of time working on them, it turns out that this similarity wasn’t due to informed consensus, but rather that everyone appears to have more or less recycling Romer’s 1927 skeletal, right down to the limb pose! I don’t want to name names, but you can see Romer’s skeletal below, and if you Google “dimetrodon skeletal” you can see for yourself just how pervasive the habit of “taking direct inspiration” from Romer’s skeletal has been.

The Iconic Dimetrodon, from Romer's 1927monograph

I expect people will want to know if this should be the new base-look for all Dimetrodon species, but unfortunately it’s hard to say at this point. Dimetrodon is a genus with a dozen or so valid species (depending on who you ask) spread over 20+ million years. Those species range in length from under a meter to giants more than five meters long! In short, Dimetrodon species could have had a lot of diversity in their backs, sails, etc., and it will take more more to find out. But I do feel comfortable saying that at the least Dimetrodon grandis looked quite different from the Romer-cloned version we’ve been using for most of the last century.

Thanks to Permia: I also want to take a moment to thank the team at Permia, as I quite simply would not have tackled this skeletal without their initiative. Their vision for a company that embraces both science and style is more than just glib marketing talk; they’ve been extremely supportive throughout the processes, understanding that restoring extinct animals is hard work, and sharing in the ride when it takes us on surprising twists and turns as to what we think an animal looked like (I certainly didn’t expect to end up with such a different view of Dimetrodon when I started!).

If for no other reason than this I would recommend supporting them. I’ll have more to say about Permia (and their products - I’ve been wearing prototypes of their shirts for a couple of weeks) in another post coming soon, but if you’re interested you can check them out right now on their Kickstarter campaign. It’s well worth a look.

]]>Taking a 21st century look at DimetrodonYou should be reading The Tyrannosaur ChroniclesScott HartmanFri, 03 Jun 2016 19:09:47 +0000http://www.skeletaldrawing.com/home/you-should-be-reading-the-tyrannosaur-chronicles528201651bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:574a074407eaa010521c3d77I wanted to make sure you are know about Dave Hone’s excellent new book,
The Tyrannosaur Chronicles. I’d hoped to blog about it several weeks ago,
but I had a slew of end-of-semester grading and sundry other deadlines. The
upshot of that decision is I’ve now had a chance to read the entire book,
and can say without hesitation that you are in for a treat...I wanted to make sure you are know about Dave Hone’s excellent new book, The Tyrannosaur Chronicles. I’d hoped to blog about it several weeks ago for the UK launch, but I had a slew of end-of-semester grading and sundry other deadlines. The upshot of that decision is I’ve now had a chance to read the entire book, and can say without hesitation that you are in for a treat.

Now I know what you’re thinking: “Who would write a book about tyrannosaurs? They’re so utterly boring!”. Despite the millstone* of writing about Earth’s most famous predators and their kin, Dave does a great job of making the topic fascinating. He covers all aspects of tyrannosaur anatomy, biology, and the relationships of the entire group. He also has a knack for conveying the science to non-specialists in a manner that is approachable, but doesn’t water down the story or cut down on the wonder of scientific discovery. The text isn’t heavy on technical terms, and the ones he does use are introduced to the reader.

The book is as up-to-date as you can make a book with a 6+ month lead time between final text and publication. It captures all of the modern ideas about the group, right down to the fuzzy T. rex skeleton on the cover.

Speaking of which, that’s my feathered T. rex skeletal on the cover! So to be forthcoming I want to be clear that I did the illustrations for the book. The team at Bloomsbury were kind enough to put together a budget to license my images, but the relevant part for you, dear reader, is that I was paid up front, so I make the same amount whether the book hits #3 on the New York Times bestseller list or finds itself in the bargain bin by July.

So I hope you believe me when I say this is a book that dinosaur enthusiasts will love. Not because of the illustrations (though naturally I’m rather fond of them), but because it’s an excellent way for a general reader to get a deeper understanding of paleontology in general, and tyrannosaurs in particular. That’s not to say the book could be read by anyone - the text would certainly be too dense for my 8 year old daughter. But I think that an advanced middle school reader or an enthusiastic high school dinosaur fan should be able to enjoy it. In fact one of the reoccurring thoughts I had while reading the book was how dearly I would have loved to have this book in high school (another reoccurring thought I had was how excited-yet-freaked-out I’d have been to see illustrations and an illustrator’s note by my future self).

The book is/will be available in all of the usual physical and digital formats. It’s launched in several markets, but it looks like in the U.S. you can only get the digital version (and some paperback copies on the Amazon marketplace). The official launch, in hardback and paperback reaches these shores on July 5th.

If you or someone you know enjoys a good popular account of science (and dinosaurs, in particular), you should run-don’t-just-walk to your nearest bookseller or online retailer and pick up a copy for yourself.

*I am totally trolling Tom Holtz at this point.

]]>You should be reading The Tyrannosaur ChroniclesDeinocheirus - Therizinosaur or hadrosaur mimic?Scott HartmanFri, 10 Jul 2015 06:56:36 +0000http://www.skeletaldrawing.com/home/deinocheirus-therizinosaur-or-hadrosaur-mimic710201551bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:559e9a3be4b03dbf291f07e1When the skull and body of Deinocheirus were revealed there was a lot of
talk about how much it looked like a hadrosaur. I did not really agree with
this analogy, as the upright posture and large, clawed hands seemed to
indicate that it was an ornithomimid trying its best to be a therizinosaur
rather than a hadrosaur. Now I'm not so sure...

When the skull and body of Deinocheirus were revealed there was a lot of talk about how much it looked like a hadrosaur. I did not really agree with this analogy, as the upright posture and large, clawed hands seemed to indicate that it was an ornithomimid trying its best to be a therizinosaur rather than a hadrosaur. Now I'm not so sure.

Restoring the skeleton of Deinocheirus was something of a treat compared to more difficult taxa. The two recently described skeletons (one adult and one subadult) combined with the type specimen meant that almost every part of the animal is known. There was a lot of overlap between the two specimens, so cross-scaling between elements was quite easy, as was adjusting for ontogenetic changes in the proportions of the vertebrae. The skeletal reconstruction published with the Nature paper nails the proportions pretty well. Maybe that's faint praise when they had two really nice skeletons, but it's sadly uncommon in skeletals that accompany technical publications.

One thing I spent a lot of time on while producing this skeletal reconstruction was the articulation of the vertebral column. The results of course were weird - any attempt to restore Deinocheirus was doomed to weirdness of course, it's just an odd duck. But I no longer agree with my own first impressions of the animal. First off, I'm not convinced that Deinocheirus actually walked with the pelvis tilted up like early reconstructions suggested - the pelvis lacks the adaptations seen in therizinosaurs that would suggest habitually being tilted upright. Also, when the tail vertebrae of the adult are carefully placed in a neutral articulation, they don't show any more of an upright curve than other "ordinary" theropods*.

The back vertebrae do emerge at a high angle, but they also curves back down dramatically; combined with the tall neural spines of the sacrum and posterior this leads to the "humpback" look that is becoming familiar. But why would Deinocheirus do such a thing? My best guess is that it's being a hadrosaur-mimic in the back - with the strong down curve and the high neural spines it could support a thicker neck musculature for holding up that meter-long skull at the end of such spindly vertebrae

You can see that reflected in my skeletal. I also wanted to add that I don't think the tall neural spines supported a sail, nor do I think it supported a fatty hump. I think it was mostly there to support its musculature and provide better leverage. In particular, note how large and curved the front part of the ilium is (aka the preacetabular ala)? In other animals that would support the iliocostalis muscles, and if that's the case here it would support powerful muscles running up the back that would occupy at least half the height of the tal neural spines in front of the hips. As the neural spines decrease in height there would be a transition to the neck musculature (and perhaps long nuchal ligaments) to support the head on the end of that long neck.

Tl;dr for paleoartists: there would be more of a hump than a sail, but probably not a fatty one.

So there you have it. Sometimes my own initial impression following a quick read of a publication changes when I'm forced to do a detailed skeletal reconstruction. I still think Deinocheirus is a wonderfully weird critter, but in a lot of ways the initial "hadrosaur-mimic" moniker ended up being more accurate than "therizinosaur-mimic".

Edit: For another interesting analogy, go check out this post by Andrea Cau comparing Deinocheirus to Spinosaurus. Though I'm not convinced of the overall proportions of Spinosaurus yet, he raises interesting parallels between them in having enlarged neural spines, long heads at the end of long necks, and fish eating.

*The juvenile specimen does seem to show some extra curvature, but the back end of the sacrum emerges at a different angle, so it looks like the difference comes out in the wash.

]]>Deinocheirus - Therizinosaur or hadrosaur mimic?Mosasaur Tails - "Teaching the Controversy"Scott HartmanWed, 01 Jul 2015 18:46:41 +0000http://www.skeletaldrawing.com/home/mosasaurs-teaching-the-controversy51bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:55941be4e4b012c9a35f2904Mosasaurs have become all the rage lately with the release (and immense
popularity) of Jurassic World. Purely by coincidence I had a commission for
a mosasaur, Tylosaurus pembinensis. I hadn't done a mosasaur before (or any
lizards), but I'm reasonably familiar with squamate osteology so I figured
it wouldn't be nearly as far "out there" as say doing a skeletal of an
actinopterygian fish. But it turns out that when it comes to their tail
fins, science is still in the middle of telling the mosasaurs' tale...

The Jurassic World Mosasaurus making short work of a shark

Mosasaurs have become all the rage lately with the release (and immense popularity) of Jurassic World. Purely by coincidence I was commisioned to do a skeletal of a mosasaur, Tylosaurus pembinensis, for a museum display. I hadn't done a mosasaur before (or any other lizards), but I'm reasonably familiar with squamate osteology so I figured it wouldn't be nearly as challenging as doing a skeletal of say... an actinopterygian fish.

A "traditional" serpentine mosasaur, copyright Dan Varner

The bones weren't overly challenging, but the soft tissue proved to be a bit more exciting. Recent workers, especially publications by Lindgren and colleagues, have looked at vertebral mobility and specialization, caudal articulation, and a couple of impressive specimens with skin impressions and have significantly revised the traditional view of mosasaurs as serpentine sea-snake analogs.

It's clear that at least a couple of mosasaurs had a hypocercal tail fin (a bi-lobed tail where the bottom part is larger), and it's been hypothesized based on phylogenetic positioning that many more mosasaurs had them to one degree or another as well. If so then many (if not most) taxa adopted a semi-carangiform or full carangiform swimming style, where the body is quite stiff and the tail provides all of the propulsion.

Alas, Tylosaurus is not one of the the genera that has skin impressions from the tail fin region, though there are scale impressions known from other parts of the body. So what evidence is there to go on? Tylosaurus does have a downturn in the caudal region, and pretty significant vertebral specialization. For these reasons as well as phylogenetic proximity to other mosasaurs with bilobed tails I tentatively endorse the hypocercal tail interpretation; though Tylosaurus does not appear to have been a true open-sea cruiser, it does appear to have the caudal series to supported a hypocercal tail. You can see the resulting skeletal reconstruction in the non-dinosaur skeletal gallery here.

But I want to make clear that this isn't a universal opinion. After posting an initial version to my Facebook page there was a lot of discussion on it, including useful feedback by Mr. Marine Reptile himself, Mike Everhart (who incidentally runs the very useful Oceans of Kansas website). Mike made some excellent observations on tail anatomy, some of which necessitated changes to the orientation of the chevrons in the skeletal reconstruction. He also is not currently persuaded that Tylosaurus had a bilobed tail. He thinks the tail angle should be more shallow, closer to 30 degrees (I've restored it at ~40 degrees), and he thinks that instead of a hypocercal tail that it may have had a continuous "paddle", not unlike the lovely Dan Varner illustration above.

At this point I am still persuaded by the hypocercal tail model, although there's definitely a bit of gray here even assuming a bilobed tail. It's possible that the angle of the tail should be closer to Dan's preferred 30 degree orientation, though I note that with the updated chevrons there shouldn't be a problem with a lack of clearance between them when putting the tail into a 40 degree bend (which is already lower than the preserved tail of Platecarpus, which does seem to have a problem with chevron-to-chevron contact). It's also possible that the top portion of the tail could be a bit smaller, like that seen Prognathodon, though note that Tylosaurus is more closely related to Platecarpus than to Prognathodon.

But I also want to emphasize that science is constantly in a state of revision. We don't have that many direct skin impressions to work from here, and it's certainly possible that there could be more than one origin of bilobed tails in Mosasauridae, in which case a wider range of earlier taxa might lack them. And while "certainty" can be nice for feeling good about an illustration, in fact it's really great that there are different interpretations out there, as these disagreements help drive researchers to find new data, or new ways to analyze existing data to try and resolve them.

So in the interest of "teaching the controversy" on a subject where one actually exists, I decided to make the following image:

The top image has the tail angle and fin modified to match the more traditional view articulated by Mike Everhart. The bottom version restores Tylosaurus with a fin closer to that interpreted for Platecarpus by Lindgren et al. (2010), though with a less extreme tail flexure. The middle versions are where I bound my own "best-guess" interpretation from the evidence at hand. The second from the bottom is the version you will find in the skeletal gallery, but anything between the middle two would be utterly plausible in my estimation..

So if you are going to illustrate Tylosaurus, feel free to follow my lead. Or that of other workers with differing interpretations - at the least these images more or less establish the range of scientific plausibility for tail flukes. Like any other skeletal my Tylosaurus will be subject to revision if/when more data allows. And always remember, the fact that scientists don't agree with one another is a feature of the system, not a bug.

]]>Mosasaur Tails - "Teaching the Controversy"Catching up: Books, plushies, and a welcome to Gizmodo readersScott HartmanSun, 08 Mar 2015 20:13:19 +0000http://www.skeletaldrawing.com/home/catching-up-books-plushies-and-a-welcome-to-gizmodo-readers131201551bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:54cd6588e4b0f6cd6831cb28It's been a very busy year, and as a result it's awhile since I updated the
blog, There are several smaller items I want to cover before I get to
meatier topics, including a book I contributed to, an adorable
Velociraptor plushie, and the #SciArt Twitter Storm.It's been a very busy year, and as a result it's awhile since I updated the blog, There are several smaller items I want to cover before I get to meatier topics, including a book I contributed to, an adorable Velociraptor plushie, and the #SciArt Twitter Storm.

First up, a welcome to visitors from Gizmodo, who wrote a fun article on the "Twitter Storm" put together by Glendon Mellow, Kalliopi Monoyios, and Katie McKissick over at the Scientific American Symbiartic blog. For those that missed it, a number of artists that work on the frontier of science and art posted a large amount (one might call it a storm) of their work on Twitter under the #SciArt hashtag. Of course the fun thing about Twitter is that even if you missed it you can still browse through the posts here. If you like science and art and want to brighten up your day it's worth taking a look.

Next up, I want to talk about the lovely paleo plushies made by Rebecca Groom. She does some amazing work, and maintains scientific accuracy in a challenging medium. Rebecca was generous enough to send me one of her hand-crafted poseable "soft-sculpt" Velociraptor as thanks for my (trivial) role of providing an anatomical basis for some of her work, and it's so cool I had to share. Also, any of you looking for great birthday/holiday gifts for the special dinogeek in your life really ought to check Rebecca's work out (you can find her Etsy store here). To the right you can see where mine currently perches, watching over me as I work on new skeletal reconstructions (or grade papers, or write up research or...you get the idea).

Continuing the theme of "free stuff people sent me", I also wanted to mention Dinosaurs of the British Isles, by Dean Lomax and Nobumichi Tamura. I got a copy (I contributed several skeletal drawings, along with Greg Paul and Jaime Headden). I've flipped through all of it, and I have to say that if you are interested in British dinosaurs it's the most complete treatment of the subject I've seen to date, including quite a lot of photographs of specimens that were not widely available previously. Unfortunately Amazon only carries secondary resellers for U.S. customers, but interested parties can also grab it from Siri Scientific Press.

That largely clears my backlog of items I meant to cover last year. Hopefully I can find time to get into some issues regarding spinosaurids (both Spinosaurus and Baryonyx), dinosaur motion, and other goodies I've had planned but not enough time to write up yet.

See you soon!

]]>Catching up: Books, plushies, and a welcome to Gizmodo readersAquatic Spinosaurus - The authors respondScott HartmanFri, 19 Sep 2014 00:03:53 +0000http://www.skeletaldrawing.com/home/aquatic-spinosaurus-the-authors-responsd918201451bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:541b6f7be4b0e98b8ca831ceAs most of you reading this will know, I've written two posts on
Spinosaurus - the first one questioned the proportions of the composite
skeleton that recently gained fame through a paper in Science, the second
one discussing a photo that has been used for and against those
proportions. In the comments section on the second post Nizar Ibrahim wrote
a length response, which (with his kind permission) I would like to elevate
to a full post. As is often true in these debates there are parts I agree
with and others I disagree with, but I will address those at a future date.
For now I think it's only fair to give their comments the floor...

The skeleton in question, from Ibrahim et al., 2014.

As most of you reading this will know, I've written two posts on Spinosaurus - the first one questioned the proportions of the composite skeleton that recently gained fame through a paper in Science, the second one discussing a photo that has been used for and against those proportions. In the comments section on the second post Nizar Ibrahim wrote a length response, which (with his kind permission) I would like to elevate to a full post. As is often true in these debates there are parts I agree with and others I disagree with, but I will address those at a future date. For now I think it's only fair to give their comments the floor:

Hi Scott,

We are writing to clarify some aspects of the new skeletal reconstruction of Spinosaurus.

It is with a certain sense of surprise that we found out that, a few hours after publication some people thought they had solved all the mysteries of Spinosaurus (without examining the original material that is).

It has been brought to our attention that your “corrected” skeleton, assembled within a day or so of our publication, has suggested to some that the actual reconstruction, based on the fossil material, was “fishy”. That is not the case.

All the bones used in the digital model were CT scanned using the same parameters. The proportions of the digital skeleton are correct, according to our identifications. The new remains come from a site with just one individual (also remember that there are only 2 other associated dinosaur skeletons from the Kem Kem assemblage mentioned in the literature, it’s definitely not the kind of place where lots of associated skeletons are found) and additional remains of the same animal were found at the site on return expeditions, including partial spines, teeth and other elements. Note also that the thin sections we made represent the same ontogenetic stage (that includes the first remains collected and those collected on later expeditions).

In summary we have evidence for one skeleton, one individual, and one ontogenetic stage. One other thing that many people seem to have missed is that Stromer's "Spinosaurus B", almost certainly associated material (see Stromer's account), shows the same axial/appendicular proportions. Several elements of Spinosaurus B overlap with our material – which in turn overlaps with the holotype.

Let’s look at the methods you used in your reconstruction. Measurements are subjective: if you want to compare the anteroposterior length of D8 to that of the ilium you have to take into account the landmarks we used to measure the vertebrae. This detail was omitted from the table legend - we are measuring from rim to rim, not including the anterior condyle. You suggested that the measurements of the hind limb and the pelvic girdle do not match those of the vertebrae: can this be a consequence of the fact that you used different landmarks? This could significantly affect the proportions. Also, keep in mind that the neotype bones have crushing and distortions, asymmetry, etc that were not removed (we wanted to include these imperfections in the finished model). Some of these distortions, for example the medial/lateral crushing/compression of the distal femur, make it look different (narrower) from the less crushed Spinosaurus B distal femur in posterior view (while by contrast the lateral views are very close) – this is relevant to some other posts online that pointed to the more “slender” profile of our femur compared to "Spinosaurus B". Also, in the 3D model, the femur is not hanging straight down - it is angled outward/laterally slightly and so foreshortened slightly in lateral view, making it look shorter.

One other word of caution: too much is being made of photographs of the specimen in Italy, which were taken before the specimens were fully prepared in Chicago (preparation made them smaller by removing matrix at the articular ends), and also before identifications were made to place the bones on the skeleton in different locations than the Italian photodepicts. Also, some camera angles create distortions. It was a rough draft, but people now seem to be attempting to get data from it...

Copyright Marco Auditore

For an independent reconstruction effort, also see the skeletal reconstruction by Marco Auditore (on the Theropoda blog);Marco is part of our team and, using the same data set, independently obtained a reconstruction that matches the proportions of the digital skeleton.

We will detail our methods in upcoming papers. Let me just say that we went to great lengths to ensure that the different specimens were sized correctly - we examined the material many times, from the tiniest zygapophyses to the most fragmentary rib pieces. We examined hundreds of bones referred to Spinosaurus, and gathered a surprising amount ofinformation from isolated elements, some of which overlap with our remains. The “core” reconstruction rests on the neotype and holotype (which are very close in size).

We have also gathered information from numerous specimens of other spinosaurids from Europe and Asia, including unpublished material currently under study; this includes an articulated c2-d4 series of Suchomimus that matches the cervical proportions in Spinosaurus rather well (the neck/skull proportions in our model also take into account Stromer’s material), as well as additional juvenile, sub-adult and adult material of spinosaurids. We also know from several lines of evidence that the vertebrae of "Sigilmassasaurus" belong to Spinosaurus – much of this will be published soon.

We are not saying that our reconstruction is 100% perfect – of course it isn’t, and I don't think this claim has been made by one of the authors - but paleontologists and paleoartists in particular should finally accept that there is no such thing as a "final word" in dinosaur reconstructions, weight estimates and behavioral interpretations. Look at Tyrannosaurus, Quetzalcoatlus or Diplodocus reconstructions and count the number of changes in posture and proportions and interpretations (scavenger, not scavenger, necks held low, necks held up, terrestrial stalkers, fish eaters etc etc). All we can do as paleontologists is present a reconstruction that best fits the available data. And then it is refined as more material comes to light. If we find a long legged Spinosaurus in Morocco, we will tell you, rest assured. But right now we have two associated skeletons with the same proportions. And if we find more forelimb material, we will refine our model if necessary.

We have been very transparent about our approach and have presented strong evidence in favor of our interpretations. The skull of Spinosaurus has "fish eating" written all over it, one of the best matches for the bone compactness profile is a penguin, and we have paddle like feet and a "river of giants" full of car sized coelacanths, giant lungfish, sawfish and many other aquatic forms. Suggesting that Spinosaurus took full advantage of this, and reduced its hind limbs in the way other lineages have done as they spent more and more time in the water is the best hypothesis we have – taken together, all of the evidence suggests that Spinosaurus spent a substantial amount of time in the water. We are working on a monograph thatwill include detailed descriptions and more measurements, as well as large amounts of unpublished data. So you will soon have access to more data to inform your beautiful skeletal drawings.

Nizar Ibrahim, Simone Maganuco, Tyler Keillor, Matteo Fabbri.

]]>Aquatic Spinosaurus - The authors respondSpinosaurus fishiness part deuxsize estimatesScott HartmanSun, 14 Sep 2014 04:42:35 +0000http://www.skeletaldrawing.com/home/there-may-be-more-fishiness-in-spinosaurus913201451bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:54147d5fe4b08db18090e5e6In my previous post on the proportions of the new Spinosaurus material I
argued that the pelvis and legs are not nearly as reduced in size as the
composite skeletal in Ibrahim, et al., (2014) implies.
Theropod-worker-extraordinaire and all-around swell guy Thomas Holtz
mentioned a photo (seen at left) that could serve as a sort of independent
visual line of evidence that the pelvis and legs of the new Spinosaurus
specimen are shorter than other theropods, and potentially shorter than I
calculated from the supplementary data. I think it's worth taking a closer
look...

In my previous post on the proportions of the new Spinosaurus material I argued that the pelvis and legs are not reduced in size to the extreme degree portrayed in the composite skeletal in Ibrahim, et al., (2014). In the comments section of that post theropod-worker extraordinaire and all-around swell guy Thomas Holtz mentioned a photo (seen at left) that could serve as a sort of independent visual line of evidence that the pelvis and legs of the new Spinosaurus specimen are shorter than other theropods, and potentially shorter than I calculated from the supplementary data. Checking our assumptions (including mine) is part and parcel of science, so let's take a look.

Andrea Cau wrote an excellent post on his blog wherein he makes a strong case that the remains of Stromer's "Spinosaurus B" specimen and the newly described material by Ibrahim et al. are not themselves chimeras, instead accurately recording theropods with smaller-than-usual pelves and hind legs. This is an objection that has been raised before to try and explain away any oddities of the original Stromer material, and has been informally raised regarding the newly described neotype specimen.

I find Cau's argument, as well as the taphonomic description of Ibrahim et al. persuasive, and I think it's very likely that the two specimens are not, taken individually, composites of multiple individuals. Jaimie Headden warns that mixing the two specimens together might result in a chimera, especially when you start referring isolated remains, some of which have been referred to other taxa (e.g. Sigilmassassaurus). I think he makes a good case, but that doesn't impact the scaling of the pelvic girdle and hind legs, which in the new specimen really are reduced compared to other spinosaurids (and other theropods in general).

This should not be contentious - to my knowledge no one is arguing that the legs of Spinosaurus are unreduced. My own "correcting" of the composite skeletal proportions still results in a theropod with a reduced pelvic girdle and hind limbs (certainly reduced compared to my original skeletal reconstruction). Given the other data from isotopes, sensory pits on the schnoz, etc., there is also a case to be made that the limb reduction correlates with increased time spent in or around the water. The question is to what degree, and that's where the numbers published by Ibrahim et al., don't seem to add up to their reconstruction of a quadrupedal, Ambulocetus-grade level of aquatic behavior.

Cau posted another image (seen directly above) which was taken at less of an less angle than the one featuring Homo sapiens for scale, so let's work with that image. On first visual examination there's no getting around it, that's a small pelvis and hind limb! But that's not really in dispute, the key is to what degree is it reduced? In the paper the ilium in the skeletal is portrayed as slightly shorter than 3 dorsal vertebrae. Glancing at the photo it should be obvious that the pelvis is not that short, but what we really want is a more precise estimate. Measuring the length of the individual centra in the photo can actually be pretty tricky; between distortion and the vertebrae sitting at semi-oblique angles it's hard to ensure you aren't making them longer than they really are. In measuring the three longest centra relative to the ilium I get a scalar of between 3.6 and 4.0. I would attribute that variation to the inherent imprecision of the technique, but notably it's in the same range as I previously calculated from the authors' measurements in the supplementary table S2 (which is 3.9).

But wait, there's more! Stare hard at the limb proportions for a bit. Notice anything strange?

If you said "neither the femur nor the tibia appear shorter than the ilium" then you get a gold star. Why does that matter? Because in the official composite skeletal both limb elements are portrayed as shorter than the ilium; in the case of the femur it's portrayed as dramatically (~17%!) shorter than the ilium.

Scribbled on by me, but still cribbing images from Cau.

Don't take my word for it, pop the file into ImageJ or Photoshop and try it yourself. At right is the same image with my own measuring points added for reference.Given that the ilium is restored as 71 cm in length the femur certainly appears substantially longer than the published length of 61 cm.

Of course now we are in the realm of questioning whether the measured and published lengths are correct. It may seem like this is a case of who are we going to believe, the paper or our lying eyes, but it's really not that simple. Measuring photographs is not reliable - foreshortening and parallax can bedevil well-meaning folks who take measurements from photos. Another possibility is that the femoral head could be broken in these photos and turned upright, leading to the appearance of extra length. I'm not convinced of that, but there does appear to be a break in the upper 1/4 of the femur that might shrink the femur by ~5-10% when fully seated (though it would still be noticeably longer than portrayed in the official composite skeletal).

The simple fact of the matter is that measuring photographs that other people have taken is just not sufficiently precise to establish the exact proportions of a specimen. So have I accomplished something aside from increasing our uncertainty? That would actually be an OK goal, as I want people to understand that this isn't easily resolved. One thing these photos are not evidence of is the neotype possessing legs and a pelvis as small as shown in the Ibrahim et al., composite skeletal - taken at face value these photos seem to show legs that are even longer than I originally suggested.

But really it's the ambiguity that is important. Most of the data in the Ibrahim et al. paper are solid and probably won't prove to be controversial. But the interpretation of a quadrupedal, semi-aquatic theropod that parallels early whales is a major claim, and it (mostly) rests with the accuracy of the skeletal reconstruction (both the proportions of the limbs and the estimated center of gravity stem directly from it). And that is where I feel the paper falls short; an Ambulocetus-grade spinosaur is an extraordinary claim, but it fails to provide extraordinary evidence for the proportions and center of gravity that make or break this claim.

The authors, their preparators and scientific illustrator(s) went to great lengths to scan in existing bones, model the lost bones from Stromer's specimen, etc., but when it comes to documenting how these disparate specimens were scaled together into a composite skeleton the paper simply says they were "size adjusted". The supplement provides an "order" that was followed in scaling (neotype specimen>models of Stromer's specimen>isolated bones>bones from other spinosaurids). But that's not very informative. I and several others have noted, for example, that the centra on the neotype presacrals appear more elongate than in photographs of Stromer's Spinosaurus B. How is this reconciled in the composite? The composite skeletal shows the pelvic girdle improbably high on the mostly incomplete sacral vertebrae (which makes the legs functionally shorter) - how was that deduced? These are the sorts of things we need to know if we are to favor the early-cetacean model over a "giant-stork" model, but at best we are left with too little information to test the idea, and at worse measurements that suggest the skeleton isn't modified to the extreme levels implied in the paper.

Important Note:

I find it sad that I need to write this, but I fear parts of the internet have run amuck. I've seen people attack the credibility of either the journal Science or the authors of the paper. DO NOT DO THIS! There is nothing at all to suggest malfeasance, and knowing most of the people involved either from personal experience or by word of mouth I will happily vouch for them as good, honorable individuals. I realize that some people on the internet feel very strongly about how Spinosaurus "should look", but don't make the mistake making the issue personal. The fact of the matter is our wishes won't affect the proportions of Spinosaurus one iota - all we can do is try our best to uncover them and then let the chips (data, not cow) fall where they may.

]]>Spinosaurus fishiness part deuxThere's something fishy about the new SpinosaurusScott HartmanFri, 12 Sep 2014 05:38:54 +0000http://www.skeletaldrawing.com/home/theres-something-fishy-about-spinosaurus911201451bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:54127413e4b0b768abd9f15dToday, after weeks of rampant internet speculation the new-look
Spinosaurus was revealed. And it certainly didn't disappoint: the paper by
Ibrahim et al. musters a range of evidence from bone density, bone isotope
data, facial innervation, osteology, etc., to suggest that Spinosaurus not
only was a fish-eater (i.e. piscivorous) but was adaptive to that lifestyle
to a greater degree than other known spinosaurids. Not only do they claim
that Spinosaurus spent most of its life swimming in the water with
adaptations that would rival early whales, but Ibrahim et al. specifically
claim that the altered limb proportions would require Spinosaurus to have
been an obligate quadruped on land, a first for a theropod.
Unfortunately, there seems to be something fishy with those new
proportions...

Today, after weeks of rampant internet speculation the new-look Spinosaurus was revealed. It certainly didn't disappoint: the paper by Ibrahim et al. musters a wide range of evidence from bone density, isotope data, facial innervation, osteology, etc., to suggest that Spinosaurus not only was a fish-eater (i.e. piscivorous) but was adaptive to that lifestyle to a greater degree than other known spinosaurids. Not only do they claim that Spinosaurus spent most of its life swimming in the water with adaptations that would rival early whales, but Ibrahim et al. specifically claim that the altered limb proportions would require Spinosaurus to have been an obligate quadruped on land, a first for a theropod.

I'm afraid I am not here to surprise you with an updated skeletal reconstruction. But I do have some preliminary observations, and after checking the scaling of the composite skeleton I'm afraid there appears to be something fishy with the proportions (see what I did there?).

First off, note that when looking at Figure 2 from the paper (shown at top) they color in a lot of "Spinosaurus" material, which might give you confidence in the proportions they use to reconstruct the skeleton. However, if you read the supplemental data (and as with any paper I highly recommend you do) you will find the Supplemental Figure S3, which has a whole lot of additional colors. In order to interpret this you need to know that the red and rust-orange represent the newly designated neotype and the older (now destroyed) Stromer specimens, but about all of those other bones? Yellow is referred isolated remains (i.e. they aren't informative in terms of proportional scaling), the green elements are based on other spinosaurids (e.g. they are not from Spinosaurus) and the blue are "inferred" (e.g. restored, not based on actual fossils).

I of all people won't begrudge the authors' for inferring missing bones, and they are to be commended for the supplemental figure, which so clearly labels which bones are based on which specimens in a visual and easy to understand diagram. But when boiled down to the bones that impact the scaling of the specimen there is a lot less data to work with than a reader might infer from Figure 2 up at the top of this post. In terms of proportions, most of the newly available data only pertains to the pelvis and the hindlimbs. I created a (rough) schematic diagram to illustrate what we knew prior to this publication from Stromer's material (smaller skeletal) and what we have to base the proportions on with Stromer's material plus this new specimen (NOTE: I haven't changed the proportions or shape of the new pelvic and hindlimb elements, this is a schematic diagram).

Ibrahim et al. (2014) shift the tall-spined "caudal" vertebrae back to being a posterior dorsal, and they move the next tallest caudal almost all the way to the anterior part of the tail, in contrast to the positions that have been recently suggested. This results in a much shorter "retro-look" sail and a rather skinny but flexible tail. That may well be correct, but what I want to focus on is the pelvis and hindlimb proportions. The authors' provide a wonderful table (S2) with measurements of individual elements of the neotype specimen, which is naturally the first thing I went to check when I saw how radical the new interpretation was. And that's where we run into trouble.

How can we know how large the pelvis and the hind limbs are relative to the rest of the animal in a composite skeleton? The best way to tell is to scale them against the dorsal column, and luckily the neotype specimen (FSAC-KK 11888) has several vertebrae. Table S2 in the supplemental data section reports that D8 is 18 cm long. It also reports that the length of the ilium is ~71 cm in length, or nearly 4 times the length of D8 (3.94 to be precise).

As it happens you can use ImageJ or Photoshop to check the linear proportions of those elements with their respective measurement tools, and here is where something fishy happens, as the ilium in the reconstruction from the paper is much too small relative to the vertebrae from the same specimen. In fact it needs to be increased about 27% (e.g. x 1.27) to match the published length. And it's not just the ilium that is wrong; the rest of the pelvis and the entire hindlimb is off, and they are off by about the same amount, suggesting it's the reconstruction and not the measurements that are in error.

I've "corrected" the size of the pelvis and hind limb so that they match their published size relative to the dorsal vertebrae, and it makes a pretty big difference. Not only do the hindlimbs look more in line with other theropods, but the deeper pelvis would also impact the center of gravity calculations (by shifting them back). I haven't had a chance to look at the scaling of the cervical or caudal series in depth, but assuming that Table S2 is correct then the appendicular skeletal proportions published in the paper cannot be right. At the very it least it calls into question the idea that Spinosaurus was an obligate quadruped on land.

Original at the top, corrected at the bottom.

Now I want to say a few words of caution. Given the heightened popularity of Spinosaurus (especially on the interwebz) I fear this will lead to exuberant and irrational skepticism of the Ibrahim et al., paper. I am not advocating the wholesale rejection of their data - the new specimen certainly helps fill in some osteological gaps, and the taxonomic revision they undertook was desperately needed. Likewise, the bone density data (and previously published isotope work) make a strong case for Spinosaurus eating fish and spending most of its time in and around the water. In other words, it's an important contribution to science. And I am certainly not trying to impugn the integrity of anyone - I am only saying that there appears to be a significant error in the scaling, something I've certainly done myself. But given the facts available it appears that the proportions of the skeletal in the paper cannot be correct, and so the locomotive and ecological interpretations that depended on the proportions must be questioned.

Also, note that I will definitely have to revise my own skeletal reconstruction. There are other issues that need to be resolved - for example, the skeletal reconstruction in Ibrahim et al. reconstructs all of the dorsal centra as far longer than tall, which is in contrast to my reconstruction. It's also in contrast to the surviving photographs of Stromer's original material, but at least some of the centra in that photo have been restored. It may be that there is a transition in the dorsal series, but without more work that's pretty ambiguous. In short, there is quite a bit of work to be done.

Hopefully I'll be able to revisit the skeletal with this new data in hand sometime soon. In the mean time, remember that we are always taking a chance when we illustrate poorly documented fossil taxa. And that's ok, because revision is part of the secret sauce that makes science work.

]]>There's something fishy about the new SpinosaurusGuanlong time!Scott HartmanMon, 08 Sep 2014 05:02:26 +0000http://www.skeletaldrawing.com/home/guanlong-at-last96201451bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:540bb925e4b0372b63c2ef6cIt's been a long time coming, but here at last is the promised skeletal of
Guanlong wucaii, as selected by you the readers in the first ever "Choose
my next skeletal" poll. You may be wondering what took me so long; several
things conspired against this skeletal...It's been a long time coming, but here at last is the promised skeletal of Guanlong wucaii, as selected by you the readers in the first ever "Choose my next skeletal" poll. You may be wondering what took me so long (one or two individuals were pointed enough to ask that outright). One thing you should know straight off - Guanlong was actually a late addition to the poll on my part, as I didn't have as much data on it as many of the other specimens. Since it was known from two quite excellent individuals and had been described I figured it wouldn't be too challenging. Famous last words, right?

Yes, it's really here!

But first, here is the long awaited Guanlong wucaii skeletal. As we've seen in other reconstructions it has a long head, but it's also a bit longer necked than I had anticipated. Even more surprising is how robust the remarkably complete forelimb is. In most other ways it seems like a typical basal tyrannosauroid, only 'turned up to eleven' via the lovely crest on the skull.

So with two excellent skeletons preserved why was there difficulty? The original (and only) description by Xu et al. in 2006 was in Nature, which makes sense given how sensational the find of a crested basal tyrannosaur was at the time. While high-impact journals like Nature and Science are great for disseminating important new discoveries (and aren't bad for the authors' careers) they also have strict page limits, which precludes the sort of detailed osteology you would get in a large monograph - the sort of thing I rely on to do a skeletal of a specimen that I haven't been able to measure and photograph myself.

Xu et al., 2006, Supplemental Fig. 2.

Even combing through the supplementary material the authors could only figure some of the bones from the adult specimen of Guanlong (the juvenile has, well, juvenile proportions, so was of limited use restoring the adult). Most of the images were of the appendicular skeleton (the arms and legs), which is certainly useful but if you don't get the proportions of the vertebral column right you can't capture the basic body proportions of an animal. In short, I was unable to do the skeletal based on the (so far) only published paper.

Luckily as the summer dragged on I got a bevy of assistance from (among others) David Hone, which was greatly appreciated. I dare say that without additional photos (with scale bars!) I would not have been able to solve some of the proportional mysteries I was faced with. Of course the usual summer items piled up as time went by (commissions, research, teaching, family). But now it's done, and I do hope it's been worth the wait.

]]>Guanlong time!Smackdown: Supersaurus vs. Giraffatitan and Diplodocussize estimatesScott HartmanTue, 22 Jul 2014 21:10:49 +0000http://www.skeletaldrawing.com/home/smackdown-supersaurus-vs-giraffatitan-and-diplodocus721201451bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:53cde663e4b00a63fc0bffcfThis entry was inspired by a post at the always-excellent SV-POW. They
compared the size (and neck length) of Supersaurus, Brachiosaurus and
Diplodocus. In a stroke of serendipity I read their post as I was reworking
my skeletal of the largest specimen of Diplodocus, NMMNH 3690 formerly
known as Seismosaurus. Let's see if that changes anything... This entry is inspired by a similarly themed post at the always-excellent SV-POW. They compared the size (and neck length) of Supersaurus, Brachiosaurus and Diplodocus. In a stroke of serendipity I read their post as I was reworking my skeletal of the largest specimen of Diplodocus, NMMNH 3690.

NMMNH 3690 is the dinosaur previously known as Seismosaurus hallorum. Most workers have since agreed that it's just a large specimen of Diplodocus, though many still insist upon giving it a distinct species name, D. hallorum. As my coauthors and I noted in 2007, there aren't actually any characters that justify that separation. Even the infamous ischial "hook" was shown to be nothing more than incomplete preparation by Lucas and colleagues a year before our paper. While final word will have to wait until someone does a specimen-level phylogenetic analysis of diplodocines, I will continue to refer the specimen to D. longus for the time being.

But enough taxonomy, the point is that there are larger specimens of Diplodocus to use in this comparison! And while the NMMNH specimen tragically lacks any cervicals, if we scale up the neck from other specimens of Diplodocus we can get a good idea of just how long this genus can stretch out to.

Now that I've rescaled missing elements, I get a full length of just under 32 meters. Which is a really big animal, but far short of the 38-50 meter lengths that were tossed around in the 1990s. Obviously we can't know exactly how long the neck was on this specimen, but assuming that it retained similar proportions to other adult Diplodocus specimens we would be looking at an 8 meter long neck.

That is in the same ballpark as Matt's estimate for Brachiosaurus, but of course the eponymous North American brachiosaurid isn't known from many more published cervicals than NMMNH 3690 is. So instead of Brachiosaurus I decided to use the better known Giraffatitan. There are some reasonably complete cervical series for Giraffatitan and much better scaling constraints all around. For everyone's favorite specimen on display in Berlin (HMN SII) I get a neck length of almost 9.5 meters. Another specimen of Giraffatitan (HMN XV2) has a tibia that is reported to be 13% longer, so assuming isometric scaling we would be talking about a neck length of 10.8 meters, which is pretty darn long!

How long you ask? It's about the same length as you would get scaling up Alamosaurus to the largest tibia that has been referred to it (which puts it up in the range of giants like Puertasaurus and Argentinosaurus), so about as long as the neck of any titanosaur. Up till now it would appear macronarians may lay claim to the longest neck (and potentially total length) of any dinosaur.

Wait, what's that up in the sky? Well heck, I guess it couldn't be Supersaurus since getting any adult sauropod off the ground would fraught with...difficulties. But Supersaurus is indeed the taxa we want to examine in this neck-size measuring contest.

At the Wyoming Dinosaur Center I was fortunate enough to work on the most complete specimen of Supersaurus, which had much better representation of the neck. As a result I feel confident in estimating the neck of the WDC specimen as almost 11 and a half meters long. Of course the type specimen from BYU is larger yet. In our 2007 paper we diagnosed "The Spaceship" specimen, BYU 9024 as being either the 10th or 11th vertebrae of the neck, which makes it roughly 6.5% longer than the equivalent vertebrae in the WDC specimen. So to the best of my abilities I would estimate that the neck of the BYU Supersaurus is 12.14 meters in length, a bit smaller than the 13.3 meters Mat come up with in the SV-POW blog.

Why the difference? Since Matt is working from a single neckbone he was understandably looking for an entire sauropod neck series that can be scaled up or down based on the BYU cervical. But the WDC specimen shows that as you get closer to the head the individual neck vertebrae get disproportionately smaller than in other diplodocids.* So while Supersaurus had a heck of a neck, I can't see it stretching out quite as long as some previous estimates (which put it up in the 15 meter range).

If you made it this far you deserve to see what all this looks like. So here are most of the specimens we've been talking about, with my 6 year old daughter and myself for scale:

We've looked at some pretty large dinosaurs today; some of them are among the biggest creatures to ever walk the Earth. But to keep things in perspective, that's a blue whale at the top of the image. It's scaled to be a large well-fed specimen of 30 meters and around ~170 tonnes, far from the largest individual ever reported. And while several of the biggest sauropods may have been a bit longer than the biggest whales, notice that you could fold up all four of these sauropods and shove them inside the same amount of space. That's HUGE.

* Why should Supersaurus have anterior cervicals that drop off in size so rapidly? One possibility is that the the atlas/axis complex may have a maximum functional length to properly support the muscles that turn and position the head. If so that could place a developmental constraint on how rapidly cervical length can increase anteriorly. But this is just spitballing into the evo-devo wind.

Addendum: Based on Mike Taylor's question below I double checked the scaling on Giraffatitan and it was slightly too large. As a result I've updated the image and the text, with the cervical length of HMN SII revised from almost 10m to 9.5, and the neck of the larger HMN VX2 revised down from 11.2 down to 10.8 meters. See discussion in the comments for other details.

]]>Smackdown: Supersaurus vs. Giraffatitan and DiplodocusAnd the winner is...Scott HartmanMon, 17 Mar 2014 20:08:31 +0000http://www.skeletaldrawing.com/home/and-the-winner-is317201451bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:53274e3be4b01248455c678fFirst off, I want to thank everyone who participated, we ended up with over
1000 votes (though not necessarily 1000 voters, as we'll see below). There
were several lead changes, but in the end a suspiciously strong showing for
one dinosaur lost out to an even more suspicious last minute route by
another dinosaur.
So without further ado, that (winning) dinosaur is...

First off, I want to thank everyone who participated, we ended up with over 1000 votes (though not necessarily 1000 voters, as we'll see below). There were several lead changes, but in the end a suspiciously strong showing for one dinosaur lost out to an even more suspicious last minute route by another dinosaur.

It should be noted that after lamenting the lack of interestSauroposeidon was garnering Saturday (when it could only muster 7th place on 44 votes) it had a ridiculously good last 24 hours, nearly tripling its vote total to 127 votes. I'm not sure where the last minute contingent of Sauroposeidon supporters came from, but they were no match for the cabal of voter(s?) that stuffed the ballot in favor of Guanlong.

To the right you can see the final vote tally - Guanlong, which after two and a half days of voting was holding down a respectable second place with 82 votes ended with an improbable 347 votes, quadrupling its vote total in the last 24 hours.

The fact that both Sauroposeidon and Guanlong showed much stronger gains on the website poll (which was anonymous) than on Facebook or DeviantArt (both require logins) suggests that a small number of voters were following the "Vote early, vote often!" matra for their favorite dinosaurs (well, at least the "vote often" part).

I have to say I'm really rather surprised that there was this degree of interest in the outcome. I didn't lay down any ground rules on how to vote, so Guanlong will be the next skeletal reconstruction I finish (though not the next skeletal I post...). I had no strong personal preference, my only concern is that everyone feel like their votes matter; as a result next time I'll take steps to prevent ballot box stuffing to quite this extent.

Anyhow, there should be a surprise or two later this week, aside from the end-of-the-week posting of the Guanlong skeletal, so check back for more soon!

]]>And the winner is...Update on skeletal drawing votesScott HartmanSat, 15 Mar 2014 18:57:46 +0000http://www.skeletaldrawing.com/home/update-on-skeletal-drawing-votes315201451bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:5324a2bce4b0fb8bb1ede468We're about halfway through the vote to determine what my next skeletal reconstruction will be, so I tallied up all the votes from the previous post, Deviant Art, and the Skeletal Drawing Facebook page. Currently Yutyrannus is holding the lead, although several dinosaurs are still in striking distance.

Vote totals as of noon EST on March 15th

Looking over the data (closing in on 600 votes already) it's clear that different venues favored different dinosaurs. For example Argentinosaurus and Protoceratops are the current winners on Facebook, but they can't keep up with theropod mania on the other two polls. It'll be interesting to see if there are any lead changes before tomorrow night.

I'll announce the winner on Monday, and do the skeletal drawing in the coming week, along with one or two other surprised (as time allows).

So here is the deal: Spring break is coming up and I plan to do a skeletal reconstruction, so I thought I'd try something fun and let you, my loyal readers, choose which animal I'll restore. I've created a list of taxa for which I already have the data (and in some cases began scaling and preliminary work) to choose from.

Vote for your favorite from now through Sunday!

Poll now closed. The winner will be announced later Monday.

]]>Europe's Shield: The most complete European ankylosaurScott HartmanSat, 25 Jan 2014 21:42:57 +0000http://www.skeletaldrawing.com/home/europelta51bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:52e42267e4b01b78d94cc3abLate last year Europe got a brand-spankin' new ankylosaur, Europelta
carbonensis. It's the most complete ankylosaur yet known from Europe
(unless you consider Scelidosaurus to be a basal ankylosaur rather than a
basal armored dinosaur). Let's take a look at the anatomy of Europelta,
with an emphasis on what we know (and aren't so sure of) when it comes to
reconstructing its armor.Late last year Europe got a brand-spankin' new ankylosaur, Europelta carbonensis. It's the most complete ankylosaur yet known from Europe (unless you consider Scelidosaurus to be a basal ankylosaur rather than a basal armored dinosaur). It also is going to help clear up some questions about the family tree of ankylosaurs (and especially basal nodosaurs) but that research has only been presented at SVP so far, so you'll have to wait for the paper to learn more.

A rigorous Europelta sans armor - brrrrr, he must be cold!

Speaking of papers, if you look at the scientific description of Europelta in PLOS ONE you will notice that the proportions of my skeletal reconstruction and the one in the paper are very similar. This is not in fact a coincidence, or even an example of two people independently coming to the same conclusion. Instead it results from the simple fact that I worked up a skeletal reconstruction with senior author Jim Kirkland about a year ago. You may wonder why my skeletal didn't end up in the paper - it turned out there was more work to be done on it (some new interpretations of the armor, a desire to have a top view skeletal, etc.). So Mark Loewen worked up his own skeletals utilizing some of the cross-scaling I'd done between the type and referred specimens.

That's ok by me though - I got a nice acknowledgement in the paper for my efforts, and I got to retain control of the copyright for my version of the skeletal. PLOS ONE requires all images they publish be made available under a CC BY license, which is very good for Open Access but not always so good for the illustrators that donate their work to such publications (not that it's ever stopped). It also gave me a chance to make some much needed tweaks to the armor of my skeletal before I released it.

A lot of times differences between reconstructions are swept under the rug or ignored, but those issues impact paleo artists, and those who simply want to know more about dinosaurs but don't have time to read each and every scientific paper that comes out, so I wanted to make sure to examine a few of them.

In this case there are quite a few differences between the armor I've restored here and that published in the original description. I've spoken with Jim and Mark and they actually already updated some of the discrepancies (in the paper they only show two rows of armor scutes on the neck, but it should have shown three). That's not a knock on Mark's efforts - restoring the armor of ankylosaurs can be a ridiculous test of your patience and organizational skills. Not too long ago when reconstructing Scelidosaurus I ran into similar problems, and eventually resorted to coloring in each individual scute as I drew them (coded by row) to keep the whole thing straight. And in that case I was working from an articulated specimen with the armor intact!

Despite those updates, there are still some differences in how I've reconstructed the armor. First and foremost I've simply reconstructed Europelta as being more flat-topped (and possibly somewhat wider) than Mark has. This has the effect of moving more of the scutes "upwards" on the body, onto the top of the back (rather than curving down the sides). This is more inline with articulated skeletons of other ankylosaurs, but of course basal ankylosaurs and nodosaurs are generally not known from fully-articulated skeletons, so this isn't a cut-and-dried assumption (I favor it, but clearly it's not universal).

Desperate measures were taken when reconstructing the armor of Scelidosaurus.

Second, Mark's version shows the small armor scales going further down the body, especially in the shoulder region. This may be totally correct. When restoring Edmontonia I and others generally stop illustrating the armor scales at the level of the lowest armor scutes. This appears to make sense since the famous articulated AMNH Edmontonia specimen shows exactly this. BUT! It still may not be correct, as there simply isn't preserved skin below that area (i.e. the specimen was excavated down to the skeleton below the scutes). Thus it's certainly possible that the small armor scales could have continued further down the body or limbs, and I know at least a couple of ankylosaur workers who feel that the taphonomy of some sites supports this very thing.

If that turns out to be the case, then the armor scales may not have a well-defined border as is commonly shown in most reconstructions. Indeed, there is little reason to think that the armor scales (or even the larger scutes) had a color that was massively different from the rest of the animal - in animals today with such scutes (such as alligators) there is no clear-cut differentiation in the coloration of the living animal. Something to think about the next time you try your hand at illustrating an ankylosaur.

]]>Europe's Shield: The most complete European ankylosaurSauropod Gallery Overhauled!Scott HartmanThu, 23 Jan 2014 18:23:05 +0000http://www.skeletaldrawing.com/home/sauropod-gallery-overhauled51bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:52e142c2e4b040775131a4d8Let's start out 2014 right, with a bunch of new and overhauled sauropod
skeletal reconstructions. All of the reconstructions of your favorite
four-legged dinosaur behemoths (and some of their smallish ancestors) have
been brought up to date. For more on this and a look at some of the
anatomical changes that have been incorporated into this overhaul click
beyond the fold to check it out.I'd like to offer a belated welcome to 2014. To start the new year off right, I've completely overhauled the sauropod skeletal gallery. This includes the debut of the Early Cretaceous brachiosaur Cedarosaurus and improved freshness dates (copyright) on all of them. You will no longer find a revision date older than 2013 (and really, 2012-2013 is about the oldest date you should accept if you want to make sure a skeletal is properly revised). The Great Skeletal Repose that started with theropods in 2011 has now reached sauropods (and their "prosauropod" cousins).
Alamosaurus sanjuanensis
Apatosaurus ajax
Apatosaurus louisae
Barosaurus lentus
Brachiosaurus altithorax
Brontosaurus excelsus
Camarasaurus lentus
Cedarosaurus weiskopfae
Diplodocus carnegii
Diplodocus longus

The new pose shows the sauropods in a slow amble (which turns out to be a rather brisk walking speed), but not doing anything so energetic that it should cause controversy.

In addition to the repose, several anatomical updates have now been "rolled out" to every critter. What this means to you, aside from knowing they are as up-to-date as I can make them, is that all of the sauropod skeletals now follow a consistent set of anatomical interpretations. While I hope to get several extra posts (and a publication or two) out of those changes, I will highlight the major items artists may wish to be aware of:

1. Plantigrade feet: Almost all modern work on sauropod biomechanics have found them to have plantigrade hind feet (where the foot bones are held closer to horizontal) with a padded backing, yet most skeletal reconstructions continue to illustrate them walking on their tip toes. Now the feet reflect the modern understanding of sauropod anatomy.

2. Following research I presented at SVP in 2012, having plantigrade hind feet but digitigrade "hands" has a material impact on the orientation of the vertebral column. This has several consequences, including necks that are more upright without needing extreme flexure at the back-neck juncture, and tails that exit the pelvis horizontally rather than arcing up into the sky (this has important functional implications, but more on that some other time).

3. Neck muscles have traditionally been restored as very minimal, often citing birds as the reason. It turns out that bird necks are actually far more muscled than many people assumed, and bifurcated neural spines in particular seem to indicate rather generous neck muscles over the base of the neck. These changes, along with increasing the size of the muscles that run from the coracoids to the neck on the bottom are now reflected in the silhouettes.

4. Finally, I've continued to bulk out the base of the tails to accomodate a more realistic mass for the leg-retracting caudofemoralis musculature. In addition to reviewing dissections, this change is based on work by Scott Persons and Phil Currie and conversations with Heinrich Mallison, and is something I've discussed previously here.

There are a few additional nips and tucks, but these are the major changes, and will probably see their own expanded posts at some point. For those of you who have contacted me to ask about higher resolution versions of my skeletals, this overhaul will also allow me to start offering them as a high-resolution booklet soon(TM). In the mean time go check out the full-sized gallery.

]]>Sauropod Gallery Overhauled!Lythronax: Tyrannosaur troublesScott HartmanSat, 09 Nov 2013 22:43:22 +0000http://www.skeletaldrawing.com/home/lythronax-tyrannosaur-troubles119201351bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:527e865ee4b0f4289e509b91This was an exciting week for tyrannosaur fans, as a new tyrannosaurine was
named (Lythronax) and new fossils of Teratophoneus were revealed.
Eagle-eyed visitors to the Skeletal Drawing theropod gallery probably
realize that they've seen two of these skeletals before, but it may not be
the two you would expect.

From left to right: Teratophoneus, Lythronax, & Bistahieversor

This was an exciting week for tyrannosaur fans, as a new tyrannosaurine was named (Lythronax) and new fossils of Teratophoneus were revealed. Eagle-eyed visitors to the Skeletal Drawing theropod gallery probably realize that they've seen two of these skeletals before, but it may not be the two you would expect. Read on for a good lesson in always labeling your files clearly.

Teratophoneus was done as part of the revamp of the UMNH dinosaur halls. It incorporated the data published this week, but since Teratophoneus had already been described I was able to show off the skeletal while remaining mum on which parts were new and which were inference. TheLythronax skeletal was also produced a couple of years ago, but I was a bit less lucky on Lythronax, and it is here that the story takes an entertaining turn.

Given Lythronax's close relationship to Bistahieversor I quite reasonably used parts from it to help constrain the poorly-known postcrania. Better yet, because the two shared so much of the restored postcrania I went ahead and created a skeletal of Bistahieversor at the same time. In fact there was a time when I assumed they would end up as the same animal (or at least the same genus). And that's what got me in trouble.

Tired of labeling my two year old Lythronax skeletal "Wahweap tyrannosaurine" (and not yet knowing it would get a new name) I labeled a copy of it Bistahieversor perhaps a year ago. And then this June I revamped my website. Unfortunately while batch-converting skeletals to get them ready for the skeletal galleries I grabbed the wrong "Bistahieversor" skeletal, thus prematurely showing off the Lythronax skeletal under the wrong name.

I realized the mistake in late summer and considered swapping in the correct skeletal, but some of you are really observant and I was concerned someone would catch the switch. Instead I just stayed pat until this week, when Lythronax was named. So now the skeletals are properly labeled, but it's not actually Lythronax that you haven't seen before, but rather my skeletal of Bistahieversor, which can now regain it's proper place.

]]>Lythronax: Tyrannosaur troublesNew and improved galleries!Scott HartmanSat, 26 Oct 2013 18:58:32 +0000http://www.skeletaldrawing.com/home/new-and-improved-galleries1026201351bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:526c0954e4b0b725baaf0de5For those of you wondering why the pace of content has slowed down, it's
because I entered a PhD program in paleontology at the University of
Wisconsin-Madison this fall, and I lost what was left of my free time. But
that's not to say that there hasn't been substantial work going on behind
the scenes of SkeletalDrawing.com!
First and foremost, there is a new skeletal gallery featuring some of my
non-dinosaur reconstructions. "Non-dinosaurs" is admittedly a pretty broad
category, and indeed it features everything from the proto-dinosaur
Silesaurus to crocodylomorphs, turtles, mammals, and even the basal
tetrapod Ichthyostega.
For those of you wondering why the pace of content has slowed down, it's because I entered a PhD program in paleontology at the University of Wisconsin-Madison this fall, and I lost what was left of my free time. But that's not to say that there hasn't been substantial work going on behind the scenes of SkeletalDrawing.com!

The reason for this hodge-podge is that most of my career has been spent working on dinosaurs, so these phylogenetic odds and ends have shown up when I was commissioned to do them for specific projects (e.g. the overhaul of the UMNH's fossil displays). Someday I hope to flesh out those groups enough to break them into separate categories, but for now if you are looking for a skeletal that doesn't happen to be a dinosaur you'll have to wade through a morass of animals that aren't closely related. At least they are posted now!

Along with the new gallery, all of the galleries have undergone substantial improvement in terms of usability. For starters, you can now link to a particular skeletal, whereas before the images did not have unique URLs. So if you want to talk about Stan the T. rex on a forum somewhere you can now link directly to that image (with proper credit, of course!).

This also means that you no longer have to browse through the galleries to learn if a specific animal is there - you can now use the search function that is available in the left-hand column on each page of my website. Previously it would discover if said animal was present, but it couldn't link you directly to the reconstruction.

The switch to unique image URLs allows another benefit that will be coming soon(TM). I will be adding an alphabetical index under the skeletal galleries dropdown, so those of you who don't care for the search function can instead browse through an alphabetical list of taxa and click on a link to be taken directly to the image in question. I'm doubtful that I will get this launched this week, since I'll be busy in Los Angeles at the Society of Vertebrate Paleontology's annual meeting, so look for it to go live in early November.

There is other exciting news to come soon, including the a look at the juvenile Parasaurolophus recently published by Farke et al., and of course the long-suffering mass estimate post on Spinosaurus. I'll also be introducing a couple of new article formats designed at speeding up the pace of new articles. Look for it all in the next month!

Update: In a fit of productivity I powered through all the links needed to make the Skeletal Index, so if you prefer to read through a list rather than browse a gallery or use the search bar you can now do so.

]]>New and improved galleries!Mass estimates: North vs South reduxScott HartmanSun, 07 Jul 2013 20:04:04 +0000http://www.skeletaldrawing.com/home/mass-estimates-north-vs-south-redux77201351bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:51d99436e4b07e30233feb4eI have good news and bad news - the bad news is today is not the day you
get a general estimate of the mass of Spinosaurus. I know, I know, and I'm
sorry. Here's the good news - in preparation for a deeper look at the
challenges of estimating the mass of Spinosaurus, I've produced far more
rigorous mass estimates of Tyrannosaurus and Giganotosaurus from GDI, and I
got some surprising results. Jump below the fold to see who is bigger (and
why I think this is so).

I have good news and bad news today - the bad news is this is not the post where you get an estimate of the mass of Spinosaurus. I know, I know. And I'm sorry. Here's the good news: in preparation for a deeper look at the challenges of estimating the mass of Spinosaurus, I've produced far more rigorous mass estimates of Tyrannosaurus and Giganotosaurus from GDI, and I got some surprising results to share.

First, a word on that Spinosaurus post - I've heard from several of you that there is a degree of anticipation for it, and I apologize for the delay. That said, you're going to get a much better post in exchange for your patience. My original intention had been to do a more generic look at scaling up different types of theropods to the length of Spinsosaurus, which would not have been very precise. Even worse, since it would have relied on other people's mass estimates it would have been comparing mass estimates derived from different methodologies, which threatened to make the whole process an act of futility.

Instead you will be getting mass estimates I've generated directly from my own skeletal reconstructions. The mass estimates I'm sharing today were produced using Graphic Double Integration (GDI), a technique that lets you estimate the volume of complex 3D objects by averaging many cross-sections together. If you are unfamiliar with the process, you can think of it as taking a balloon animal and using math to average it into a more normal oval-shaped balloon of the same volume to make it easier to measure. I won't go into detail on how to perform a GDI analysis, because the SV-POW team has already written up a really good tutorial here, which you should definitely read if you want to do your own GDI analysis.

First: the reveal:

Back when I posted the original North vs South comparison I wrote up some general thoughts on the skeletals including:

3) Sue almost certainly had a higher mass than the Giganotosaurus type specimen, as tyrannosaurs seem to have broader torsos for their size.

4) So...that large isolated Giganotosaurus jaw? It's not really clear how much bigger that individual is, because there isn't perfect linear scaling between it and the type specimen (the isolated jaw is proportionately a bit deeper). My "best fit" version indicates an animal about 6.5% longer than the type. That would result in an animal over 13 meters in length, and also one that would be heavier than Sue.

I certainly hit point number three on the head, but it appears I was a bit too hasty when it came to proclaiming that there was evidence that MUCPv-95 was heavier than Sue. The reason this occurs can be seen in the top view silhouettes I show above (which, by the way, are the very images I used, so you have the "original data" so to speak). Tyrannosaurs have almost comically wide abdomens (and mine is not as broad as some other workers and some mounts show), while Giganotosaurus has the typical allosaur-grade torso.

I'm sure many of you will want at least a few more details, so here is another quick-hit list of items you may find of interest:

1) I used 46 equally-spaced sections front to aft. The tiny forelimbs only have a few cross-sections, while the hind legs have 10.

2) I added extra skin around both skeletals to avoid the "trying to make them as skinny as possible" concern (more on that in a future post).

3) The thighs and upper half of the forearms are measured as part of the torso.

4) I used a specific gravity of 1.0 (same as water) for the limbs and tail, and 0.9 for the neck and torso (remember that the torso includes part of the denser upper limbs in this GDI) . The head uses 0.8 to account for the sinuses and empty space in the mouth.

5) Although Tyrannosaurus seems likely to have had stronger calves I used the exact same muscle reconstruction to try and make the comparison more of an apples to apples affair

6) I'm sure that some will claim that Giganotosaurus should have a wider torso or head, but the skull is already substantially wider than in Acrocanthosaurus and matches up with more recent reconstructions of the skull, like the one you see here. Also note that if anything the torso should be smaller up front due to the diminutive pectoral girdle.

7) I must reiterate, the lower jaw fragment of MUCPv-95 does not come from an animal that is 8% larger than the type. In fact it honestly could be from an identically-sized animal that just has a more robust dentary, so scaling it up 6.5% (in linear dimensions) should if anything be seen as the upper bounds.

Conclusions:

As near as I can tell, despite Tyrannosaurus and Giganotosaurus appearing similar in size in side view, there is little question that T. rex is actually the larger theropod based on known specimens. To be fair, there's only one good specimen of Giganotosaurus, and it took most of a century to find Sue, so it's certainly possible that as additional specimens are collected we will find larger southern giants. As always, please remember we don't have a statistically valid population of specimens from any of these large dinosaurs, so we are only comparing individuals, not species.

And finally, remember that no one study has magical knowledge of the "real" mass of extinct organisms. I feel confident that the GDI analysis I've performed accurately represents the volume of my own skeletal reconstructions, but obviously it reflects my own assumptions about skeletal articulation and soft-tissue anatomy. There is still substantial variation between published mass estimates; in particular the the numbers I'm publishing here are a bit lower than those given in the recent (and excellent) paper on computational analysis of T. rex by John (of the freezer) Hutchinson and colleagues.

I'll be taking a look at the underlying reasons for that, along with the unique challenges that Spinosaurus holds for GDI analysis in my next post. When that's done I'll get around to putting up my mass estimate of the Fisher King. Now I'd best go finish those calculations...

]]>Mass estimates: North vs South reduxScaling issues - a minor irritation?Scott HartmanMon, 01 Jul 2013 19:28:50 +0000http://www.skeletaldrawing.com/home/scaling-issues-a-minor-irritation71201351bf1cd3e4b0a897bf54112b:51bf3576e4b0f16202a228fe:51d1c3d0e4b08819bd80a5daThe Super Spinosaurus? post produced some interesting conversation; in
particular Marco asked a good question about whether using the skull of the
South American spinosaurid Irritator would have a material impact on the
size of the animal. Let's take a quick look at Irritator's skull, and then
a broader look at how these sorts of questions do (or don't) impact mass
estimates.

Irritator challengeri, copyright Scott Hartman, 2013.

The Super Spinosaurus? post produced some interesting conversation; in particular Marco asked a good question about whether using the skull of the South American spinosaurid Irritator would have a material impact on the size of the animal.

In addition to that question, and in anticipation of my promised look at mass estimates in the biggest theropods, I wanted to take this opportunity to briefly look at how how these scaling issues can lead to mass estimate bloat.

If you haven't heard of Irritator, now would be the time to go read up on it. The name refers to what it sounds like - being downright annoyed at having to fix a previous attempt at preparing the skull (and discovering that some of the features were not actually real). But now that the skull is fully prepared and described, it provides the most complete articulated spinosaurid skull available. And as an added bonus it's also more closely related to Spinosaurus than to cousins Baryonyx and Suchomimus.

Above you can find my rigorous reconstruction of Irritator's skull (the dark gray area roughly represents the Angaturama snout that has been referred). Of note is that it's actually quite similar to how I've restored the skull of Spinosaurus (which was based in part on photos of unpublished specimens).

Skull reconstructions of Spinosaurus (top) and Irritator compared.

Comparing the skulls as the same snout depth, you can see that the back of Irritator's skull is relatively shorter compared to the reconstructed Spinosaurus skull. A close inspection of the snout, however shows that strictly-speaking they aren't 100% comparable. Irritator seems to have proportionately more space between the nose and the antorbital fenestra (the hole in front of the eyes). It's not clear whether this effects the overall length of the snout, but it certainly impacts which parts of the face are lengthened (i.e. Spinosaurus appears to have a more retracted nose). So you can't simply take the big MSMN V4047 Spinosaurus snout and scale it based on Irritator's skull, as there isn't a perfect fit with which to scale it.

This probably shouldn't be hugely surprising - while Irritator and Spinosaurus are fairly close relatives, they do live on separate continents and possibly at different times - there's no reason we should expect their skulls to be clones of one another.

Even better, it doesn't matter much for size estimates. Scaling my current Spinosaurus skull up to the size of the big MSMN snout yields a skull in the 163-164 cm range. Hacking off the back of Irritator's skull and pasting it onto the back of the same snout results in a head that is ~`158 cm... a difference of less than 4%.

A 4% difference in skull length translates to less than half a percent on the length of the entire animal - far less than the actual margin of error we have (mostly from unknowns in the tail length). Even better, it has no bearing on the mass estimates at all - the issue of whether the skull was a bit shorter or longer doesn't impact the torso length, that relationship is instead determined by the size of the head (and type mandible) to the type vertebrae.

Which brings me to my last point: mass estimate bloat. Whether looking at giant theropods or sauropodsthere is an almost continual creep of size estimates on the internet (and sometimes in the peer-reviewed literature) as people seem to try and find any excuse to get the largest possible number. There are several ways this happens, but one in particular that I'd like to address right now:

Remember the difference between varying proportions and scaling an entire animal up!

Because of the non-linear relationship between linear dimensions and volume, scaling up an entire animal leads to exponential growth in the mass estimate. So a T. rex that is three feet longer than Sue may weigh several tons more. But that's only true if you are truly scaling up the hole animal, not just making a skull or a tail longer.

My reconstruction of MSMN V4047, for example, is shorter than 16 meters in length. I try to be as careful as possible about not hiding the uncertainty in these estimates, so given how little of the tail is known I happily pointed out that the specimen could be anywhere from 15-17 meters (or even more) in length. But! I don't mean that you can take a mass estimate of the type specimen and scale it up to a 17 meter long animal - what I mean is that it's hypothetically possible that you can add an extra meter or two of tail to Spinosaurus. That means the mass estimate is still basically for a <16m long spinosaur that just has a couple dozen kilograms added in tail length, which is radically different from the 15-20 ton estimates you get the other way.

Likewise, it's pointless to try and scale up isolated toe bones (like UCMP 137538, a single T. rex toe bone) because we don't know the proportions of the toe bone's owner. Not only is there normal variation in a population, but with pathology the amount can vary even in the same specimen (check out both hands of Big Al, metacarpal one varies in length by almost 50%).

I'm not trying to poo poo people who are interested in maximum size. But we need a bit more rigeur when trying to establish how big they were. And exactly how big do I think they are? It's coming, I promise.

In the past I have been skeptical of claims of 50+ foot Spinosaurus specimens - and with how little we know about the tail length in Spinosaurus there is still reason for caution.

That said, science is always based on data, and sometimes the data isn't what you expected. I was reminded of this once again recently after I tweaked the scaling of elements in my Spinosaurus skeletal reconstruction. The "main" skeletal seen above (the fully restored version is in the theropod gallery) is based on a composite skeletal of the type specimen and other various referred bits. Previously I'd had the mandible scaled up too much by about 6%. After correcting I measured and sure enough, a nice 14m (46 foot) long beast.

Now please use some caution here: as you can see the composite skeletal is missing large swaths of bones. I have filled those in with bones from other relatives (e.g. Baryonyx and Suchomimus), but there's definitely some uncertainty here. Of particular note, tail length varies quite a bit in dinosaurs (as demonstrated recently by Dave Hone), and I would feel a lot better about estimating the length if we had some more Spinosaurus tail vertebrae.

Still, unless you restore an almost comically long tail the type specimen of Spinosaurus was less than 50 feet. Ah, but that's not the largest specimen! The biggest specimen referred to Spinosaurus is MSMN V4047, a giant snout that Dal Sasso et al described in 2005.

Assuming that the composite is scaled correctly and that the giant MSMN specimen scales up isometrically (which seems probable) then it would be in the range of 15.6 meters (51 feet) give or take. That's one long theropod we are looking at! Given our margin of error it's entirely possible that the MSMN specimen is actually 48 feet (or 55 feet!), but assuming it had proportions similar to that of other spinosaurids, then it seems clear that 50 foot lengths were most likely attained.

Of course length is just one estimate of size, and mass is generally considered more important. And here things get interesting. Check back this weekend for a closer look at how much Spinosaurus may have tipped the scales in life.